Powder Metallurgy.docx

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UNIVERSITI TEKNOLOGI MALAYSIA “POWDER METALLURGY”

Transcript of Powder Metallurgy.docx

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UNIVERSITI TEKNOLOGI MALAYSIA

“POWDER METALLURGY”

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1.0 INTRODUCTION

POWDER METALLURGY (P/M) is concerned with the production of metals powders and converting them to the useful shape. This process first was used by the Egyptians in about 3000 B.C. to make iron tools. It is a material processing technique in which particulate materials are consolidated to semifinished and finish product. Generally the emphasis is on the metallic materials but the principle of the processes apply with the little modification to the ceramic, polymers and variety of composites materials composed of metallic and non-metallic phases.

Nowadays P/M techniques are increasingly used to provide exceptional properties that are required in highly sophisticated aerospace electronic and nuclear energy industries. However automobile industry is the major consumer of P/M by industries (70% of the P/M market). Product like tungsten filament, tungsten carbide, porous self lubricating bearing etc. is either difficult or impossible to make by other methods. The other reason is that P/M processes of manufacturing structural components competes with other manufacturing methods such as casting, machining and forging. P/M processes minimize or eliminate the machining, and scrap losses at the same time is suited to high volume production of component. The process offer economy, saving in energy and raw materials along with mass production of quality precision component. 2.0 PROCESS PRINCIPLE AND CAPABILITIES

The traditional P/M process consists of blending the metal powders and other constituents followed by compaction to produce the desired size and shape. The green compact is then sintered by heating at elevated temperatures, preferably below the melting point of the major constituent to get product of desire density, structure and properties. The two stages of compacting and sintering are combined into a single step in pressing. Powders can also be rolled continuously and sintered to produce strips and other flat product or can be forged to get high strength finish component. Some of the limitations of die compaction and sintering in traditional P/M process can overcome by the recent developed isostatic compaction and hot isostatic compaction methods. The latter method is increasingly becoming important for the fabrication of sophisticated and advanced materials.

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2.1 Process Principle P/M process principle consists of the following operations, in sequence: RAW MATERIALS MIXING FORMING SINTERING OPTIONAL OPERATIONS (FINISHING) FINISH PRODUCT

Element or Alloy Metal Powder

Additives (graphite, die lubricant)

Mixing

Compaction

Cold – Die compacting, Isostatic, Rolling, Inj. Molding, Slip Casting Hot/Warm – Isostatic, Extrusion, Spraying, Die compacting, Pressureless sintering

Sintering

Atmosphere Vacuum

Optional Manufacturing Steps

Repressing Coining Sizing Resintering Rerolling Metal Infiltration

Optional Finishing Steps

Machining Heat Treating Steam Treating Plastic Impregnation Plastic Tumbling Oil Impregnation Shot Peening

Finish Product

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2.1.1 Powder Production (Raw Materials)

There are several methods of producing metal powders, and most of them can be produced by more than one method. The choice depends on the requirement of the end product. The microstructure, bulk and surface properties, chemical purity, porosity, shape and size distribution of the particles depend on particular process used. Particle sizes produced range from 0.1 to1000 μm.

Atomization

Atomization produces a liquid-metal stream by injecting molten metal through a small orifice (figure 1 & 2). The stream is broken up by jets of inert gas or air or water known as gas and water atomization. It is a process where a liquid is fragmented into molten droplets which then solidify into particles. This method produced 80% of all the commercial powder use in P/M process.

Figure 1: Water Atomization Process Figure 2: Vertical Gas Atomizer

Other method in atomization is centrifugal atomization, the molten-metal stream drops onto a rapidly rotating disk or cup, so that centrifugal forces break up the molten-metal stream and generate particles (figure 3). An electric arc impinges on a rapidly (about 15,000 rev/min in helium-filled chamber) rotating electrode (all contain within a chamber purged with inert gas), with centrifugal force causing the molten droplets to fly from the surface of the electrode.

Figure 3: Centrifugal Atomization by the Rotating Electrode Process

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Reduction

The reduction of metal oxides (i.e. removal of oxygen) uses gases, such as hydrogen and carbon monoxide, as reducing agent. By this means, very fine metallic oxides are reduced to the metallic state. The powders produce are spongy and porous and have uniform size spherical or angular shape. In solid-state reduction, selected ore is crushed, mixed with a reducing species (e.g., carbon), and passed through a continuous furnace. In the furnace, a reaction takes place that leaves a cake of sponge metal which is then crushed, separated from all non-metallic material, and sieved to produce powder. Since no refining operation is involved, the purity of the powder is dependent on the purity of the raw materials. The irregular sponge-like particles are soft, readily compressible, and give compacts of good pre-sinter (“green”) strength. Electrolytic Deposition

Electrolytic deposition utilizes either aqueous solutions or fused salts. The powders produced are among the purest available. By choosing suitable conditions, such as electrolyte composition and concentration, temperature, and current density, many metals can be deposited in a spongy or powdery state. Further processing–washing, drying, reducing, annealing, and crushing–is often required, ultimately yielding high-purity and high-density powders. Copper is the primary metal produced by electrolysis but iron, chromium, and magnesium powders are also produced this way. Due to its associated high energy costs, electrolysis is generally limited to high-value powders such as high-conductivity copper powders. Carbonyls

Metal carbonyls, such as iron carbonyl (Fe(CO)5) and nickel carbonyl (Ni(CO)4

) are form by letting iron or nickel react with carbon monoxide. The reaction products are then decomposed to iron and nickel, and then turn into small, dense, uniformly spherical particles of high purity.

Comminution

Mechanical comminution (pulverization) involves crushing (figure 4) milling in a ball mill, or grinding of brittle or less ductile metals into small particles. A ball mill (figure 4b) is a machine with a rotating hollow cylinder partly fills with steel or white cast iron balls. With brittle materials, the powder particles produced have angular shapes; with ductile metals, they are flaky and are not particularly suitable for P/M applications.

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Figure 4: Mixing and blending processes of metal powders. (a) crushing (b) mixing (c) hammering Mechanical Alloying

In mechanical alloying, powders of two or more pure metals are mixed in a ball mill. Under the impacts of the hard balls, the powder fracture and bond together by diffusion, forming alloy powders. The dispersed phase can result in strengthening of the particles or can impart special electrical or magnetic properties of the powders. 2.1.2 Mixing (Blending) Mixing (blending) powders is the next step in P/M processing. It’s refers to when the powders of the same chemical composition but possibly different particle size are intermingled. It is rare that a single powder will possess all of the characteristics desired in a given process and product. Most likely, a starting material will be a mixture of various grades or sizes of powder, or powders of different compositions, with additions of lubricants or binders. Some powders, such as graphite, can even play a dual role, serving as lubricant steel. Lubricants improve the flow characteristics and compressibility at the expense of reduced green strength. Mixing (blending) operations can be done either dry or wet, where water or other solvent is used to improve mixing, reduce dusting, and lessen explosion hazards. This process create advantages of P/M technology beccause of the opportunity to mix various metals into alloys that would be difficult or impossible to produce by other process. Many types of mixer and blenders are used for P/M process. Batch mixer are the most common and include drum, cubic, double cone, twin shell (V), and conical screw (rotating auger) types. The selection of the optimum mixer for a given powders requires careful consideration. Testing must be perform for each case.

2.1.3 Compacting (Forming)

Compacting is one of the most critical steps in P/M process. It’s consists of automatically feeding a controlled amount of mixed powder into a precision dies, after which it is compacted. Cold compaction is the first step in the shaping of loose powders into a product of desired form

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and sufficient strength for further handing. It is mostly done by unidirectional compaction in a die or to a lesser extent by cold isostatic pressing (CIP). More specialized techniques are injection molding and explosive compaction. Pressure range from 10 tons/in.2 (138 Mpa) to 60 tons/in.2

(827 Mpa).

The pressed powder is known as green compact. It’s an unsintered P/M compacted since it has a low strength. A schematic of unidirectional compaction is given in figure 5. In a first stage the particles are rearranged leading to a better packing. Increasing pressure provides better packing and decreasing porosity. At high pressure the individual particles are deformed and some cold welding between the particles occurs which gives some strength to the green compact. Because of the wall friction the densification of the compact is not uniform. The problem can be minimised by using lubricants and by applying a load from top and bottom simultaneously. The design of the dies is very important because it must take into account that the green product must be ejected after compaction. This limits the geometry that can be obtained by unidirectional compaction. An alternative method is cold isostatic pressing (CIP). Sealed molds of powder are loaded in a liquid inside a high pressure tank and a hydrostatic pressure is applied by pressurizing the liquid. Typical pressure are between 300 to 400 MPa. This method is useful for large, homogeneous compacts. At a given pressure, higher densities than in die compressions are reached. CIP is very useful for complex shapes but suffers from poor dimensional control.

Other methods is hot isostatic pressing (HIP), the container generally is made of a

highly-melting-point, and the pressurizing medium high temperature inert gas or a vitreous (glasslike) fluid. Common condition for HIP is pressures as high as 100 Mpa (or can be 3 times as high and the temperature at 1200ºC). the main advantages of HIP is the ability to produce compacts having almost 100% density, good metallurgical bonding of properties, and good mechanical properties. Consequently, it has gained wide acceptance in making high-quality part.

Figure 5: Powder Consolidation Cold Compaction

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Explosive compaction is a technique which is mainly used in laboratory conditions but with some possibilities for limited industrial scale applications. A shock wave is used to achieve a rapid consolidation of the power. Minimal heating is observed while high densities are obtained (up to 99 % of the theoretical density). With this technique negative consequences of sintering or hot consolidation can be avoided; amorphous structures can be preserved during compaction.

Injection moulding provides another method of consolidating powders. The method is

similar to the moulding of plastics and conventional moulding equipment can be used. Powders are mixed with thermoplastic binders and injection moulded to a required shape. Before sintering the binder is removed by thermal degradation or by solvent extraction. The method is useful for small but complex parts. 2.1.4 Sintering

The word sinter comes from the Middle High German Sinter, a cognate of English cinder. In the sintering operation, the pressed- powder compacts are heated in a controlled-atmosphere environment to a temperature below the melting point but high enough to permit the solid-state diffusion and held for sufficient time to permit bonding of the particles. Most sintering operations involve three stage and many sintering furnaces employ four corresponding zones (figure 6).

The first operation (zone 1), the burn-off or purge, is designed to combust any air,

volatize and remove lubricants or binders that would interfere with good bonding and slowly raise the temperature of the compacts in a controlled manner. The second (zone 2 & 3), or the high- temperature stage is where the desired solid – state diffusion and bonding between the powder particles take place. Finally (zone 4), a cooling period is required to lower the temperature of the products while maintaining them in a controlled atmosphere.

These three stages must be conducted in a protective atmosphere. This is critical since

the compacted shapes have residual porosity and internal voids that are connected to exposed surfaces. Reducing atmospheres, commonly based on hydrogen, dissociated ammonia, or cracked hydrocarbons, are preferred since they can reduce any oxide already present on the particle surfaces and combust harmful gases that are liberated during sintering. During the sintering operation, a number of changes occur in compact. Metallurgical bonds form between the powder particles as a result of solid-state diffusion and strength, ductility, toughness, and electrical and thermal conductivity all increase. Diffusion may also promote when different chemistry were blended.

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Figure 6: Sintering – Different atmosphere in sintering conveyor furnace

2.1.5 Optional Operation (Finishing)

P/M parts are ready to use after they have emerged from the sintering furnace but many products utilize one or more secondary operations to provide enhanced precision, improved properties, or special characteristics. Secondary operations are be performed to improve; density, strength, shape, corrosion resistance and tolerances. P/M metal parts may be subjected to other finishing operation such as:

a. Machining – for producing various geometric feature by milling and tapping (to produce threaded holes)

b. Grinding – for improved dimension accuracy and surface finish c. Plating – for improve appearance and resistance to wear and corrosion d. Heat treating – for improved hardness and strength

2.2 Process Capabilities The P/M process capabilities can be summarized as follows:

a. It is a technique for making parts from high-melting-point refractory metals and part which may be difficult or uneconomical to produce by other methods.

b. High production rates are possible on relatively complex parts using automated equipment and requiring less labor.

c. Powder-metal processing offers goods dimensional control and (in many instance) the elimination of machining and finishing operation; in this way, it reduces scrap, wasted and saves energy.

d. The availability of a wide range of composition makes it possible to obtain special mechanical and physical properties, such as stiffness, vibration damping, hardness, density, toughness and specific electrical and magnetic properties. Some of the newer highly alloyed superalloys can be manufactured into parts only by P/M processing.

e. It offers the capability of impregnation and infiltration for specific applications.

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3.0 THEORY RELATED IN POWDER METALLURGY PROCESS

Characteristic of Metal Powder The characteristics of a powder are important because they often determine the choice of a particular processing route. Powder characterization is a rather complex procedure since not only the properties of individual particles (size, shape, etc.) must be determined, but also the characteristics of the powder mass (particle size distribution, apparent density, etc.) and of the porosity in the powder mass (average pore size, pore volume, etc.). In general the following characteristics should be determined:

a. Chemical composition - the chemical composition as well as the impurity content can be determined with normal analytical chemistry methods; beyond the bulk chemical information, there is often a need to know the surface conditions of the powder (oxidation, observed organic films, surface coatings, etc.); hydrogen weight loss measurements can give an idea about the surface oxidation, while the inclusion concentration can be measured by acid dissolution; in some special cases Auger electron spectroscopy can be needed.

b. Internal particle structure - micro segregation, internal pores and precipitates can be studied with conventional microscopic techniques such as light optical microscopy and electron microscopy.

c. Mean particle size and particle size distribution - a large variety of methods to measure the particle size distribution is available; one method uses the ability of the eye to rapidly size dispersed particles in a microscope another popular method is sieving (screening) : the powder is tapped through a set of sieves with increasing mesh size and the amount of powder in each sieve is weighed; other techniques are based on the measurement of sedimentation, electrical conductivity, light scattering or even X-ray techniques for very fine powders;

d. Particle shape - a view of possible particle shapes is presented in Figure 7; the shape of a particle is very important and must be considered together with the size distribution; it can be determined by a scanning electron microscope.

Figure 7: Possible Particle Shapes and Qualitative Descriptors

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Forming (Compaction)

Decreasing of the axial stress 𝜎𝜎𝑎𝑎 during compaction

𝐹𝐹 = 𝜋𝜋𝑟𝑟2 𝑓𝑓 = 2𝜋𝜋𝑟𝑟𝜋𝜋𝜋𝜋

𝝈𝝈𝒂𝒂(𝒙𝒙) = 𝝈𝝈𝒂𝒂(𝟎𝟎)𝒆𝒆−𝟐𝟐𝟐𝟐

𝒓𝒓� Figure 8: Axial stress during compaction

Frictional forces at the wall of the compacting die restrain the compaction of the powder. With increasing distance from the face of the compacting punch, the axial stress 𝜎𝜎𝑎𝑎 , which is available for the local densification of the powder, decreases.

Influence of the density on the material properties

Calculation of Materials Properties: Figure 9: Effect of the density on materials properties

𝟏𝟏+𝝂𝝂𝝆𝝆𝟏𝟏+𝝂𝝂𝒐𝒐

= � 𝝆𝝆𝝆𝝆𝒐𝒐�𝒎𝒎

𝑷𝑷𝝆𝝆𝑷𝑷𝒐𝒐

= � 𝝆𝝆𝝆𝝆𝒐𝒐�𝒎𝒎

Where; 𝜌𝜌 - density 𝜌𝜌𝑜𝑜 - full density 𝑃𝑃𝜌𝜌 - material properties of the raw material m - powder coefficient

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Spring-back as function of compact density Figure 10: Spring-back as function of compact density Parameters influencing the spring-back – compacting pressure, compacting density, powders properties, lubricants and alloying, additions, shape and elastic properties of the compacting die. Sintering Solid state sintering

The efficiency of a sintering process is mainly influenced by the temperature, the time, the properties of the protective atmosphere, the density of the compact, the particle size and the particle shape. Solid state sintering can be divided into three (overlapping) steps (Figure 11):

a. Bonding of powder particles forming necks. b. Change of pore geometry and shrinkage of the compact. c. Isolation of pores by grain growth, elimination of residual porosity.

Figure 11: Powder Consolidation - Solid State Sintering

𝑺𝑺(%) = 𝟏𝟏𝟎𝟎𝟎𝟎.(𝝀𝝀𝒄𝒄 − 𝝀𝝀𝒅𝒅)

𝝀𝝀𝒅𝒅

S = Spring-back in % 𝜆𝜆𝑐𝑐 - Transversal dimension of the (ejected) compact 𝜆𝜆𝜋𝜋 - Corresponding dimension of the compacting die (after ejection of the compact)

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Diffusion types at sintering

The sintering process involves some mass transport. At least six different diffusion paths can be identified (Figure 12), lattice diffusion from grain boundaries, surfaces and defects, boundary diffusion from grain boundaries, surface diffusion from surfaces and vapour phase transport from surfaces. Many models have already been proposed to describe the growth of necks and the shrinkage of pores, but due to the complexity of the pores a general accepted quantitative model remains to be developed.

Figure 12: Powder Consolidation – diffusion types

4.0 THE FOREFRONT IN POWDER METALLURGY PROCESS: DRILLING OF HIGH QUALITY FEATURES IN GREEN P/M COMPONENTS Approaches based on green machining appear promising to reduce machining costs and

compete favorably with other shaping processes. Advancements in binder/lubricant technologies have led to the development of high green strength systems that enable green machining of high quality features. This study deals with the drilling of through holes in high green strength P/M components.

This process involves the machining of components while they are in their “green state”, i.e.

before sintering. The main advantage of this process is its ability to triple the production rate of the machining operations. Furthermore, green machining extends tool life. Green machining is not a straightforward procedure. Steel parts pressed to a green density of 6.8 g/cm3 have typical green strength values of 12–17MPa (∼1750–2500 psi). These values are insufficient to allow proper holding of the parts in the chuck of a lathe or a machining center and would lead to catastrophic failure during machining. However, recent developments, such as warm compaction and binder/lubricant technologies, allow us to obtain improved green strength values. Warm compaction consists in pressing a preheated powder at a temperature typically ranging from 90 ◦C to 150 ◦C to obtain green strengths about four times higher as those provided by room temperature compaction.

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Several authors investigated the possibility of machining such high green strength P/M components especially in the case of drilling operations. The machining performances of green P/M components are usually based on the surface finish and on the average width of breakouts formed near the edges of machined surfaces. The objective of this study was to improve the machining behavior of green P/M components while drilling through holes. This was achieved by using a high green strength powder system and optimizing the cutting parameters. Design of experiments (DOE) and analysis of variance (ANOVA) were used to optimize surface speed, feed rate and drill type. Experimental procedure

A powder system was produced based on Quebec Metal Powders 4601 sinter-hardenable powder (Fe–1.8 wt.% Ni–0.5 wt.% Mo–0.2 wt.% Mn) to which was added 2.0 wt.% Cu and 0.6 wt.% graphite. Lubrication was done using 0.65 wt.% of a proprietary binder/lubricant (FLOMET HGSTM) specifically adapted for high green strength and green machining. This mix was pressed into rectangular plates (10.8 cm×10.8 cm×1.6 cm) to a green density of 7.00 g/cm3.

These samples were submitted to a curing treatment in air at 190ºC for 1 h to increase their green strength and their machinability in terms of surface finish and edge integrity. Green drilling experiment

The machining operation performed on green plates was the drilling of through holes. The drilling operation was done using a computer numerically controlled (CNC) machining center (Republic Lagun, model VCM 4824). The drilling process was performed dry, i.e. no coolant was used. Thrust force measurement was performed during drilling using a dynamometer placed underneath the sample (Kistler, type 9443B). Four drill types (diameter 6.35 mm), manufactured by Kennametal, were investigated. There are two cutting parameters in drilling: surface speed and feed rate.

Since the matrix of experiments involves 64 tests, design of experiment (DOE) using orthogonal arrays and signal to noise (S/N) ratios was used. The selected orthogonal array is a L16, which allows us to reduce the number of tests to 16. Such orthogonal array allows the determination of the relative influence of each parameter studied. Moreover, the usage of S/N ratios instead of averages permits to optimize the cutting condition while minimizing the variance of the latter. The equation used for calculating S/N ratio is the following smaller the- better type, where n is the number of measurements and y is the measurement value

𝑆𝑆𝑁𝑁

= −10𝑙𝑙𝑜𝑜𝑙𝑙10 �1𝑛𝑛�𝑦𝑦1

2𝑛𝑛

𝑖𝑖=1

Series of 16 holes were drilled in the same specimen and the test was repeated on three

different plates for reproducibility.

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Table 1: Cutting parameters and levels investigated for the drilling experiments Results & discussion. Optimization of cutting parameters for drilling through holes:

These S/N ratios were averaged by parameter level to determine the optimum cutting

condition for drilling through holes in a green P/M component as shown in figure 13. The optimum cutting condition for each parameter is the closest value to zero since the desired results for each criterion is zero, i.e. minimum thrust force, minimum width of breakouts and lowest number of Ra and Rz.

Figure 13: Graph of parameter effect: (A) Thrust force, (B) Average width of breakout (C) Surface finish (Ra), (D) Surface finish (Rz),

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Table 2: ANOVA as a function of machinibility criteria Considering the results obtained from the ANOVA in table 2 above, the feed rate is

responsible for 94% of the variation of the thrust force. Therefore, a low feed rate of 0.025 mm/r is suggested for reducing the thrust force while the variation of the latter criterion is unaffected by the drill type and the surface speed.

The variation of the average length of breakouts is mainly caused by the drill type and the feed rate, which contribute for 48% and 47%, respectively. Considering the average width of breakouts, the optimum cutting conditions for the sets of parameters studied are: KWCD00461 drill type, feed rate of 0.0254 mm/r. The last criterion studied was the surface finish, which is mostly affected by the feed rate. The latter parameter is responsible for almost 80% of the variation of both the Ra and Rz criteria. Thus, a value of 0.0254 mm/r is suggested for improving the surface finish of the machined surfaces. The drill type and the surface speed showed much lower contributions on the variation of the results, i.e. approximately 10% each.

The second parameter studied was the surface speed. Within the range studied, the latter

shows a very small contribution on the final outcome of the drilling process regardless of the machinability criterion. Therefore, a high surface speed of 140 m/min is suggested for increasing productivity. The last parameter investigated was the feed rate. The control of this parameter is essential for producing high quality features in green drilling and a value of 0.0254 mm/r is suggested.

Conclusions It has been shown that high quality through holes can be drilled in green P/M steel components (FLC-4608 powder type). To increase edge integrity and surface finish, the cutting conditions suggested are the following (based on the range of parameters investigated):

1. Drill type: KWCD00461 (diameter 6.35 mm), produced by Kennametal or equivalent. 2. Surface speed: 140 m/min (7000 rpm) 3. Feed rate: 0.0254 mm/r

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Following these conditions, the thrust force measured during drilling is 107 N, the average width of breakouts near the outlet edge is 115 µm and the surface finish inside the hole is 3.7 µm and 25.3 µm for criterion Ra and Rz, respectively. The dimensional change of the diameter of holes drilled in green P/M components is identical to that measured for holes incorporated in the components during compaction. Therefore, the green machining process does not affect the dimensional change of features during sintering.

5.0 POWDER METALLURGY PRODUCT PRODUCED AND APPLICATION

Products that are commonly produced by powder metallurgy can generally be classified into five groups.

a. Porous or permeable products - Oil-impregnated bearings made from either iron or copper alloys, constitute a large volume of P/M products. They are widely used in home appliance and automotive applications since they require no lubrication or maintenance during their service life. Unlike many alternative filters, they can withstand conditions of elevated temperature, high applied stress, and corrosive environments.

b. Products of complex shapes that would require considerable machining when

made by other processes - Because of the accuracy and fine finish characteristic of the P/M process, many parts require no further processing and others require only a small amount of finish machining. Large numbers of small gears are made by the P/M process. Other complex shapes such as pawls, cams, and small activating levers, can be made quite economically.

c. Products made from materials that are difficult to machine or with high melting

points - Some of the first modern uses of P/M were the production of tungsten lamp filaments and tungsten carbide cutting tools.

d. Products where the combined properties of two or more metals (or both metals

and nonmetals) are desired - The unique capability of the P/M process is applied to a number of products. In the electrical industry, copper and graphite are frequently combined in such applications as motor or generator brushes, copper providing the current carrying capacity, with graphite providing lubrication. Similarly, bearings have been made of graphite combined with iron or copper or of mixtures of two metals, such as tin and copper, where the softer metal is placed in a harder metal matrix. Electrical contacts often combine copper or silver with tungsten, nickel or molybdenum. The copper or silver provides high conductivity, while the material with high melting temperature provides resistance to fusion during the conditions of arcing and subsequent closure.

e. Products here the powder metallurgy process produces clearly superior

properties - The development process that produce full density has resulted in P/M

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products that are clearly superior to those produced by competing techniques. In areas of critical importance such as aerospace applications, the additional cost of the processing may be justified by the enhanced properties of the product. In the production of P/M products magnets, a magnetic field can be used to align the particles prior to sintering, thereby producing a high flux density in the product.

6.0 SUMMARY

P/M metallurgy is a net-shape forming process consisting of producing metal powders, blending, compacting them in dies, and sintering them to impart strength, hardness and toughness. Compaction also may be carried out by cold or hot isostatic pressing for improved properties. Although the size and the weight of its product are limited, the P/M process is capable of producing relatively complex part economically, in net-shape form, to close dimensional tolerances, and form a wide variety of metal and alloy powders.

P/M technology was intended to bring the forefront for the engineering community, a

parts making methodology that many are not exposed to. The technology has potential to provide a method of producing almost any part that can fit in the palm of one hand. It is highly-suited for mass-production quantities, since each part is so consistent.

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[2] B.J. Moniz, “Metallurgy” 3

Edition S.I. Unit, Pearson Prentice Hall. rd

[3] Hwaiyu Geng, “Manufacturing Engineering Handbook”, Mc Graw Hill.

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[4] John E. Neely & Thomas J. Barlone, “Practical Metallurgy & Materials of Industry”, 6th

[5] Stephen L. Feldbauer, “Advances in Powder Metal Sintering Technology’, Abbott

Furnace Company St. Marys, PA 15857

Edition, Pearson Prentice Hall.

[6] Dr. James W. Sears, “Direct Laser Powder Deposition”, Lock Heed Martin.

[7] N. Tosangthum, et. al., “Sintering of 316L + Ni powder compacts”, Advances in Powder

Metallurgy and Particulate Materials (Compile by. W. Brian James and Russell A.

Chernenkoff), Metal Powder Industries Federation, 2004.

[8] R.L. Orban, “New Research in Powder Metallurgy”, Technical University Of Cluj-Napoca.

[9] B. Verlinden, University of Leuven & L. Froyen, University of Leuven, Belgium,

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[10] P. Ramakrisnan, “History of Powder Metallurgy”, Department of Metallurgy Engineering,

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[11] Etienne Robert-Perron, Carl Blais, Sylvain Pelletier, Yannig Thomas, “Drilling of high quality features in green powder metallurgy components” Department of Mining, Metallurgical and Materials Engineering, Universit´e Laval, Quebec City, Que., Canada